Question: On the first 3 quizzes of her geometry class, Jessica got an average score of 81. What does she need on the next quiz to have an overall average of 85?
Explanation: Let her score on the next quiz be $x$ The sum of all of her scores is then $3 \cdot 81 + x$ The same sum must also be equal to $4 \cdot 85$ Solve: $x = 4 \cdot 85 - 3 \cdot 81 = 97$.